Adaptive control system for machine tool or the like

ABSTRACT

An adaptive control system for a machine tool or the like includes two pairs of thrust sensors for measuring radial and axial spindle deflection and a temperature sensor for measuring spindle bearing temperature. Data processing apparatus, typically comprised of a microcomputer, is coupled to the thrust and temperature sensors and regulates the spindle bearing preload and spindle axis feed rate in accordance with the radial and axial spindle thrust. The microcomputer simultaneously regulates the percentage of oil in the oil/air mixture lubrication mist sprayed on bearing contact surfaces in accordance with bearing temperature, thereby assuring optimum machine tool performance.

This is a division of application Ser. No. 316,059, filed Oct. 29, 1981.

BACKGROUND OF THE INVENTION

This application is related to U.S. Pat. No. 4,421,443 issued to R.Woythal et al. on Dec. 20, 1983.

The present invention concerns a control system for machine tools or thelike, and more particularly to a control system for machine tools whichregulate spindle bearing lubrication in accordance with bearingtemperature and which regulates the spindle bearing preload and thespindle axis feedrate in accordance with spindle bearing thrust toassure optimum machine tool performance.

Rotating machinery, such as machine tools, or the like, usually includeone or more ball bearings or roller bearings for journaling a rotatingmember such as a spindle as in the case of a machine tool, to astationary member such as the machine tool spindlehead. It is well knownto those skilled in the art that friction between ball bearing androller bearing contact surfaces is best reduced by lubricating thebearing with a fluid lubricant, either a single fluid, such as oil orair or a lubricating fluid mixture such as an oil-air mist mixture. Anoil-air lubricating mist mixture is particularly advantageous since theair in the oil-air lubrication mist mixture serves to carry away bearingheat while the oil provides appropriate lubrication for bearing contactsurfaces, thereby assuring long bearing life.

One of the difficulties incurred in employing an oil-air mist mixture tolubricate ball bearings and roller bearing has been regulation of theamount or volume of oil in the oil-air lubrication mist mixture aspercentage of total mixture volume. Too little oil in the oil-airlubrication mist mixture results in insufficient bearing lubrication andhence premature bearing wear. On the other hand, too much oil in thelubrication mist mixture may cause the bearings to clog and overheatthereby greatly reducing bearing life.

Heretofore, regulation of the percentage volume of oil in an oil-airbearing lubrication mist mixture has been achieved by open loopregulation, that is, by manually presetting the oil and air mixingvalves. Needless to say, should the speed or axial thrust of therotating member journaled to the bearing suddenly change, then thepercentage volume of oil in the oil-air bearing lubrication mist mixturemust also be changed. Otherwise, bearing damage may result if too littleor too much oil is present in the bearing lubrication mist mixture.Additionally, should a valve clog, or if the flow of oil becomesintermittent, then there may also be an insufficient volume of oil inthe oil-air mist mixture. The present invention concerns a controlapparatus for rotating machinery which automatically regulates thepercentage volume of oil in the oil-air lubrication mist mixturesupplied to lubricate rotating machinery ball and roller bearings.

It is an object of the present invention to provide a control apparatusfor regulating the lubrication provided to rotating machinery bearings.

It is another object of the present invention to provide a controlapparatus for automatically regulating the lubrication provided tomachinery bearings in accordance with bearing temperature to assurereduced bearing temperature thereby extending bearing life.

It is yet another object of the present invention to provide a machinetool control apparatus for automatically regulating spindle bearinglubrication in accordance with spindle bearing temperature and forregulating the spindle bearing preload and the spindle axis feedrate inaccordance with radial and axial spindle deflection.

BRIEF SUMMARY OF THE INVENTION

Briefly, in accordance with the invention, a control apparatus forregulating the lubrication provided to rotating machinery roller andball bearings comprises a lubrication system for providing the machinerybearings with fluid lubrication which may either be an oil-air mistmixture or a single fluid such as air or oil. A temperature sensor, suchas a thermistor or thermistor network, senses bearing temperature andprovides an electrical signal indicative thereof to a control apparatus,such as a microcomputer. In accordance with bearing temperature, themicrocomputer automatically regulates the volume of fluid lubricationsupplied to the bearings from the lubrication system, thereby assuringproper bearing lubrication at all times.

A preferred embodiment of the invention, specifically adapted for usewith a machine tool such as a horizontal or vertical boring mill,further includes thrust sensors for sensing radial and axial spindlethrust and for generating an electrical signal indicative thereof. Thecontrol apparatus, in addition to regulating the volume of spindlebearing lubrication in accordance with bearing temperature alsoregulates spindle bearing preload and the spindle axis feedrate inaccordance with radial and axial spindle thrust to reduce bearingstress, thereby assuring optimum machine tool performance.

BRIEF SUMMARY OF THE DRAWINGS

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however,both as to organization and the method of operation, together withfurther objects and advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a block diagram of the control apparatus of the presentinvention;

FIG. 1A is an alternate embodiment of the lubrication system of FIG. 1;

FIG. 2 is a graphical representation of how bearing temperature variesin accordance with the percentage volume of oil in the oil-air mistlubrication mixture;

FIG. 3 is a side elevational view of a high speed machine tool spindleof a machine tool;

FIG. 4 is an enlarged view of a portion of the high speed spindleillustrated in FIG. 3; and

FIG. 5 is a block diagram of a modification of the control apparatus ofFIG. 1 for controlling a machine tool embodying the spindle of FIGS. 3and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a block diagram of a control apparatus 10 forrotating machinery, such as a machine tool, for regulating thelubrication supplied to machinery bearings 12 which journal a rotatingmachinery member such as a shaft 14 to a stationary member (not shown).Control apparatus 10 comprises a temperature sensor 16, typicallyconfigured of a thermistor or the like, mounted adjacent to bearing 12for providing an electrical output signal indicative of bearingtemperature. In certain instances, it may be desirable to employ a pairof thermistors to measure the temperature of the fluid (either air oroil, for example) entering and exiting the bearing for determiningbearing temperature exactly. The output signal of thermistor 16 issupplied to an analog to digital (A/D) converter 18 which converts theanalog thermistor output signal into a digital signal which is suppliedto an electronic processing circuit 20, typically a microcomputer.Microcomputer 20 is responsive to the output signal of A/D converter 18,and in accordance therewith, determines the proper volume of lubricationfluid supplied by lubrication apparatus 22 to lubricate bearing 12.

In the presently preferred embodiment, lubrication system 22 isconfigured to provide an oil-air lubrication mist mixture and includes apair of electrically controlled valves 24a and 24b, each valve beingelectrically connected to and controlled by microcomputer 20. Valve 24bis coupled between a supply of pressurized air 25b and an atomizer 26and controls the amount or volume of air admitted to atomizer 26 inaccordance with signals from microcomputer 20. Valve 24a is coupledbetween a supply of pressurized lubricating oil 25a and atomizer 26 andcontrols the volume of oil admitted to the atomizer in accordance withsignals from microcomputer 20. Typically, each of valves 24a and 24bcomprises an ASCO model TX8262208 valve manufactured by Automatic SwitchCompany, Florheim Park, N.J. Atomizer 26 atomizes the oil suppliedthereto from oil supply 25a through valve 24a with air supplied theretofrom air supply 25b through valve 24b to produce the oil-air mistmixture which is sprayed on bearing 12.

A better understanding of how microcomputer 20 regulates the percentagevolume of oil in the oil-air lubrication mist mixture may be gained byreference to FIG. 2 which illustrates the relationship between thepercentage volume of oil in the oil-air lubrication mist mixture and thebearing temperature. As can be seen, the relationship between thepercentage volume of oil in the lubrication mist mixture and the bearingtemperature is concave upwards, having a relative minimum identified bythe point X. With the knowledge that the relationship between thepercentage volume of oil in the lubrication mist mixture and the bearingtemperature is concave upwards, microcomputer 20 is programmed tocalculate the ratio of the rate of charge of bearing temperature to therate of charge of the percentage volume of oil in the lubrication mistmixture (ΔT/Δ%). If ΔT is made sufficiently small, the dT/d%, the firstderivative of the bearing temperature-% oil relationship can beapproximated. Since, from elementary calculus, the first derivative(dT/d%) of the bearing temperature-% oil relationship is representativeof the slope of the curve, and since the slope of the bearingtemperature-% oil curve of FIG. 2 is equal to zero at the point X on thecurve, it follows that dT/d% is zero at the relative minimum (point X)on the curve of FIG. 2. From the calculated values of dT/d%,mircrocomputer 20 can determine the percentage volume of oil necessaryto maintain minimum bearing temperature.

The process by which microcomputer 20 regulates the % volume of oil inthe oil-air bearing lubrication mist mixture is a dynamic rather than astatic process. Since bearing temperature does not remain constant, butvaries in accordance with such factors as shaft speed and bearing load,among others, microcomputer 20 continually monitors bearing temperaturesso that the % volume of oil can be continuously regulated to assureproper bearing lubrication. Microcomputer 20's fast processing speedallows it to respond to very rapid incremented changes in bearingtemperature, thereby assuring proper bearing lubrication at all times.

It may be desirable in some applications to lubricate the rotatingmachinery bearings with a single lubricating fluid such as oil or air incontrast to lubricating the bearings with a mixture of lubricatingfluids such as air and oil. This may be readily accomplished byempolying the alternate lubrication system embodiment 22' illustrated inFIG. 1A in place of lubrication system 22 in FIG. 1. Lubrication system22' comprises a single electrically controlled valve 24' which iscoupled to a supply of pressurized lubrication fluid 25' (which fluidmay be either a gas, such as air or a liquid such as oil) for regulatingthe volume lubricating fluid supplied to bearing 12 (FIG. 1) inaccordance with singnals from microcomputer 20 (FIG. 1). The volume oflubrication fluid carried by valve 24' from lubricating fluid supply 25'is controlled by microcomputer 20 in accordance with bearing temperaturein exactly the same manner in which microcomputer 20 controls valves 24aand 24b of lubrication system 22 of FIG. 1, since the bearingtemperature will vary in accordance with the volume of fluid suppliedfrom lubrication supply 25' in exactly the same way the bearingtemperature varies in accordance with the percentage volume of oil asdepicted in FIG. 2.

The control apparatus of FIG. 1 is well suited for use with numericallycontrolled machine tools for automatically regulating spindle bearinglubrication. The control apparatus allows higher machine tool spindlespeeds and higher spindle loads to be reached than would otherwise bepossible. Further, as detailed hereinafter, the control apparatusdescribed above, can be modified to control not only machine toolspindle bearing lubrication but the spindle bearing preload and thespindle axis feedrate which allows attainment of still higher spindlespeeds and spindle loads as well. This may be better understood byreference to FIGS. 3 and 4 which illustrate a portion of a high speedspindle assembly 100 of a numerically controlled machine tool. Spindleassembly 100 is typically disposed in a frame such as the machine toolspindlehead, (not shown) which is linearly movable on the machine toolalong an axis at a rate referred to as the spindle axis feedrate.Although spindle assembly 100 can take the form of any well known highspeed spindle, in the presently illustrated embodiment, spindle assembly100 comprises the high speed spindle assembly described in U.S. Pat. No.4,421,443 issued to R. Woythal et al. on Dec. 20, 1983 and assigned tothe assignee of the present invention. The aforementioned application isherein incorporated by reference. As described in that co-pendingapplication, high speed spindle assembly 100 comprises a spindle 110having an axially extending bore therethrough dimensioned to receive theshank 112 of a cutting tool therein. Spindle 110 is integral with theshaft of a motor 114 comprised of a stator 114a and a rotor 114b. A key115 extending from spindle 110 engages a complementary keyway in therotor (not shown) to lock the spindle to the rotor so that spindle 110rotates co-jointly with rotor 114b.

Spindle 110 extends through the case 116 of motor 114 and is journaledto the front and rear of motor case 116 by front and rear spindlebearings 118 and 120, respectively, which are each carried on spindle110 adjacent to a separate one of the ends thereof. Front spindlebearing 118 comprises a pair of ball bearings 124a and 124b,respectively, which are carried on spindle 110 between a shoulder orflange 126 and threads 127. A nut 128 engages threads 127 to urge thelower races of ball bearings 124a and 124b against shoulder 126.Adjusting the displacement of nut 128 from shoulder 126 serves to verythe force against, or the preloading on, the lower ball bearing races.The upper races of ball bearings 124a and 124b are urged against avertical wall in motor case 116 by an annular ring piston 129 which isreciprocally disposed in a piston chamber 130 within a front bearing cap132 fastened to motor case 116 by bolts 134 which are disposed throughpassages spaced equidistantly about the bearing cap circumference.

The amount of force or preloading on the upper races of ball bearings124a and 124b varies in accordance with the pressure of hydraulic fluidadmitted into piston chamber 130 through a connecting passage 136 from asource of hydraulic fluid (not shown) which is coupled to connectingpassage 136 through a pressure regulator (described hereinafter). Thepressure of hydraulic fluid admitted through connecting passage 136 fromthe source of hydraulic fluid is varied by the pressure regulator inaccordance with radial and axial spindle bearing thrust. To this end,two pairs of spindle thrust sensors 137a and 137b, respectively, whosesensors are typically comprised of a magnetic or capacitive transducer,are disposed within bearing cap 132 adjacent to spindle shoulder 126 tomeasure radial and axial spindle thrust, respectively. Referring now toFIG. 4 which is an enlarged fragmentary view of a portion of the spindleassembly illustrated in FIG. 3, to measure radial spindle thrust, onethrust sensor of thrust sensor pair 137a is vertically disposed inbearing cap 132 adjacent to flange 126 above the axis 138 of spindle110; the other thrust sensor (not shown) of thrust sensor pair 137a isvertically disposed in bearing cap 132 so as to be adjacent to flange126 below the spindle axis. To measure axial bearing thrust, one thrustsensor of thrust sensor pair 137b is horizontally mounted in bearing cap132 adjacent to the flange so as to be above the spindle axis while theother thrust sensor (not shown) of thrust sensor pair 137b ishorizontally mounted in the bearing cap adjacent to flange 126 belowspindle axis 138. The thrust sensors of thrust sensor pairs 137a and137b are connected differentially to produce a signal varying inaccordance with radial and axial spindle thrust, respectively.

The output signal produced by each of thrust sensor pairs 137a and 137b,which varies in accordance with radial and axial spindle thrust,respectively, is supplied to a control apparatus 200 illustrated in FIG.5 which controls the spindle axis rate and bearing preload as well asthe percentage volume of oil in the oil-air lubrication mist mixture.Control apparatus 200 comprises an analog to digital (A/D) converter218, for converting the analog signal from each of thrust sensor pairs137a and 137b (FIGS. 3 and 4) into a digital signal which is transmittedto a microcomputer 220 is responsive to the output signals from A/Dconverter 218 and, during intervals when the radial and axial thrusts onspindle 110 (FIG. 3) are large, as will likely occur when spindle speedsare low and the force on the cutting tool is disposed within the spindleis large, microcomputer 220 modulates the output signal supplied to apressure regulator 225, coupled between the source of pressurizedhydraulic fluid and passage 136, (FIG. 3) to increase the pressure ofhydraulic fluid admitted through connecting passage 136 to pistonchamber 130 (FIG. 3) so as to increase the force of piston 130 againstthe upper races of bearings 124a and 124b (FIG. 3), accordingly, therebyincreasing bearing preload to reduce bearing chatter. In addition,during intervals of large radial and axial spindle thrusts,microcomputer 220 also supplies an output signal to the spindlehead axisdrive motor amplifier (not shown) to reduce the axis feedrateaccordingly. At high spindle speeds when the force on the cutting toolheld in spindle 110 (FIG. 3) is likely to be much lower, therebyresulting in lower radial and axial thrusts on spindle 110 (FIG. 3)microcomputer 220, in response commands pressure regulator 225 to reducethe pressure of fluid admitted into piston chamber 130 throughconnecting passage 136, thereby reducing the preload on bearing 124a and124b (FIGS. 3 and 4). During this same interval of lower radial andaxial spindle bearing thrusts, microcomputer 220 also supplies an outputsignal to the spindlehead axis drive system motor amplifier to commandand increase in the spindle feedrate accordingly. In this way,microcomputer 220 dynamically regulates the preloading on spindlebearings 124a and 124b.

In addition to being responsive to radial and axial spindle thrust,microcomputer 220 is also responsive to machine tool spindle speed, assensed by a tachometer, or as determined by the machine tool controlsystem. During intervals when machine tool spindle speed is increased,it may be desirable to decrease bearing preload. This is readilyaccomplished by microcomputer 220 in responsive to an increase inmagnitude of the speed signal supplied thereto. Conversely, when spindlespeed decreases, microcomputer 220 increases the volume of fluidadmitted by the pressure regulated into piston chamber 130 (FIG. 4)through connecting passage 136 (FIG. 4) to increase bearing preload.

Referring back to FIGS. 3 and 4 jointly, a lubrication passage 139 isdisposed through bearing cap 132 to carry an oil-air lubrication mistmixture to bearings 124a and 124b from a lubrication system 230illustrated in FIG. 5, which is configured identically to lubricationsystem 22 described previously with respect to FIG. 1. A temperaturesensor 140 (best illustrated in FIG. 4) is disposed in bearing cap 132adjacent to bearing 124a and supplies A/D converter 218 illustrated inFIG. 5 with a signal varying in accordance with bearing temperature. Inaccordance with the digital output signal from A/D converter 218,microcomputer 220 (FIG. 5) while regulating bearing preload and thespindle axis feedrate, also supplies a pair of control signals tolubrication system 230 to regulate the percentage volume of oil in theoil-air mist mixture supplied through lubrication passage 139 tobearings 124a and 124b in the manner described previously with respectto FIGS. 1 and 2. To provide for faster lubrication system response,microcomputer 220 (FIG. 5) utilizes the output signals from each ofthrust sensor pairs 137a and 137b to sense variations in radial andaxial thrust, respectively, which in practice, precedes changes inspindle bearing temperature. By anticipating changes in spindle bearingtemperature prior to their occurance, microcomputer 220 is better ableto regulate spindle bearing lubrication.

As is further described in U.S. Pat. No. 4,421,443, spindle 110 has apair of tool gripping collets 140a and 140b, which are each integratedto a separate one of the spindle ends, respectively. Each of toolgripping collets 140a and 140b, respectively, is urged radially inwardto grip shank 112 of the cutting tool by a separate one of collet nuts142a and 142b which are each in threaded engagement with spindle 110adjacent to a separate one of collets 140a and 140b. To prevent thecollet nut at each end of the spindle from loosening during high speedrotation of spindle 110, the spindle carries a pair of hollow borecollet nut drivers 145a and 145b, the collet nut drivers each beingcarried on the spindle adjacent to a separate one of the spindle ends soas to be coaxial with, and adjacent to, a separate one of collet nuts142a and 142b, respectively. The bore through each collet nut driver isdimensioned to receive a respective one of the collet nuts. The interiorsurface of the bore through each collet nut driver, such as collet nutdriver 145a, for example, carries a set of splines 146a, which splinesare complementary to the exterior splines 146b carried on the rearwardend of each of the collet nuts, such as collet nut 142a, and arecomplementary to the exterior splines 146c carried on each end ofspindle 110 adjacent to a separate one of collets 140a and 140b. Eachcollet nut driver, such as collet nut driver 145a is slidable along thespindle between a first or inward most position at which location thecollet nut driver is adjacent to an associated one of bearing caps 132and 160, respectively, and a second or outward most position at whichlocation the collet nut driver is distal from the corresponding bearingcap. When the collet nut driver is displaced along the spindle to itsfirst or inward most position adjacent to its corresponding bearing cap,the splines on the interior surface of the collet nut driver engage theexterior splines on both the collet nut and the spindle, thus preventingthe collet nut from rotating independently of the spindle. When thecollet nut driver is slid outwardly along the spindle away from itscorresponding spindle bearing cap to its second position, then thesplines on the interior surface of the collet nut driver engage only theexterior splines on the collet nut thus permitting the collet nut andits associated collet nut driver to be threaded off of the correspondingcollet at the end of the spindle. Each collet nut driver is restrainedfrom axial movement, once slidably moved to its inward most position toengage both the spindle splines and the splines on the correspondingcollet nut, by a pair of Vlier screws 148, only one of which is shown,the Vlier screws being threaded into the spindle to extend radiallytherefrom so that each engages a circumferential groove circumscribingthe inner bore of a corresponding collet nut driver.

Proximity switches 150a and 150b are each mounted in a separate one offront and rear bearing caps 132 and 160, respectively, so that eachswitch is adjacent to a separate one of front and rear collet nutdrivers 145a and 145b, respectively. Each of proximity switches 150a and150b, respectively, is actuated when a separate one of collet nutdrivers 145a and 145b, respectively, is slidably moved inward to beadjacent to a separate one of bearing caps 132 and 160, respectively, tojointly engage a separate one of collet nuts 142a and 142b,respectively, with the spindle. When actuated, each proximity switchsupplies microcomputer 220 with a signal indicative of the engagement ofthe corresponding collet nut and the spindle. Should one of collet nutdrivers 145a and 145b be slidably moved outwardly causing acorresponding one of proximity switches 150a and 150b, respectively, tocease being actuated, then microcomputer 220 supplies an inhibit signalto the drive amplifier controlling motor 114 to prevent spindlerotation. In this manner, damage to the cutting tool as well as themachine tool operator is prevented when the cutting tool is not firmlyheld in the spindle.

The foregoing describes a control apparatus for rotating machinery forregulating the percentage volume of oil in the oil-air lubrication mistmixture in accordance with machinery bearing temperature. By regulatingthe percentage volume of oil in the oil-air lubrication mist mixture inaccordance with bearing temperature, proper bearing lubrication isassured, thereby lengthening bearing life.

Although the illustrative embodiment of the invention has been describedin considerable detail for the purpose of disclosing a practicaloperative structure incorporating the invention, it is to be understoodthat the particular apparatus shown and described is intended to beillustrative only and various novel features of the invention may beincorporated in other structural forms without departing from the spiritand scope of the invention as defined in the subjoined claims.

The principles of this invention having now been fully explained inconnection with the foregoing, we hereby claim as our invention:
 1. Anapparatus for rotatably supporting a member journaled in a frame byanti-friction bearings which comprises:sensing means in position tosense the thrust imposed upon said rotatable member and produce a signalrepresenting the sensed thrust; pressure means disposed to apply apressure to said bearings for preloading the bearings; pressureadjusting means connected to regulate said pressure for varying thepreloading of said bearings; a control connected to receive the signalfrom said sensing means representing the thrust on a rotatable member;and means connecting said control to said adjusting means for regulatingthe operation of said adjusting means in accordance with the signalreceived from said sensing means so that the preload pressure applied tosaid bearings is continually adjusted to suit the prevailing conditions.2. An apparatus according to claim 1 further comprising:lubricationmeans for applying lubricant to said bearings; temperature sensing meansdisposed to sense the temperature of said bearings and connected to senda signal representing the sensed temperature to said control; andlubricant adjusting means for adjusting the amount of lubricant directedto said lubrication means, said adjusting means being connected to beregulated by said control in response to the signal received from saidsensing means.
 3. An apparatus according to claim 1 wherein saidpressure means is an annular piston disposed in said frame in positionto apply pressure to the outer race of at least one of said bearings forpreloading said bearings; andsaid adjusting means is a pressureregulator that is adapted to regulate the hydraulic pressure directed tosaid annular piston.
 4. An apparatus according to claim 1 wherein saidrotatable member is a machine tool spindle, further comprising:feedingmeans for moving said spindle axially in a feeding movement toward andaway from a workpiece; a regulator in said feeding means for adjustingthe feed rate of said spindle selectively; and means connecting saidregulator to said control for actuating said regulator in response tothe signal received from said sensing means to adjust the feed rate inaccordance with the prevailing conditions.
 5. An apparatus according toclaim 2 wherein said rotatable member is a machine tool spindle, furthercomprising:feeding means for moving said spindle axially in a feedingmovement toward and away from a workpiece; a regulator in said feedingmeans for adjusting the feed rate of said spindle selectively; and meansconnecting said regulator to said control for actuating said regulatorin response to the signal received from said sensing means to adjust thefeed rate in accordance with the prevailing conditions.
 6. An apparatusaccording to claim 1 further comprising:a tachometer connected toproduce a speed signal representing the rate of rotation of therotatable member; and means for transmitting said speed signal to saidcontrol; wherein said speed signal is utilized in combination with saidthrust signal for determining the degree of preload pressure to beapplied to said bearings.
 7. An apparatus according to claim 2 furthercomprising:tachometer connected to produce a speed signal representingthe rate of rotation of the rotatable member; and means for transmittingsaid speed signal to said control; wherein said speed signal is utilizedin combination with said thrust signal for determining the degree ofpreload pressure to be applied to said bearings.
 8. An apparatusaccording to claim 1 further comprising:sensing means connected to sensethe temperature of the mechanism to be lubricated and to produce asignal representing the sensed temperature; a source of lubricant; anatomizer connected to receive lubricant from said source and disposed toapply such lubricant to said mechanism; a source of air pressureconnected to supply air to said atomizer for atomizing the lubricantapplied to said mechanism; and a control responsive to the signalproduced by said sensing means to regulate the volume of lubricantsupplied to said atomizer from said source and to simultaneouslyregulate the amount of air directed to said atomizer from said source sothat both the amount of air and the amount of lubricant supplied to saidatomizer are regulated by said control so that the air and oil mixtureis varied automatically to accommodate the prevailing conditions.